Vehicular mufflers are mandated by many governmental bodies to reduce the noise which emanates from an internal combustion engine. A typical construction for a vehicular muffler is one which includes an elongated body with end caps mounted on the opposed ends. Nipples on the end caps provide connections for an inlet to the muffler and an outlet from the muffler. A louver and baffle assembly is mounted within the body to muffle the noise from an internal combustion engine in a typical construction of a muffler. The body is made up of an outer wrap and an inner wrap positioned within the outer wrap. Both wraps are typically made of a sheet metal. In many instances, the sheet metal is aluminized cold rolled steel. A typical and well-known method of construction of a muffler includes the step of wrapping an inner wrap of sheet steel around a mandril, and an outer wrap is also formed around the same mandril over the inner wrap. The two wraps are seam welded. The louver and baffle assembly is inserted into the body. End caps are attached to the body to encase the louver and baffle assembly.
The construction mentioned above is taught in a number of U.S. Patents. Fukuda U.S. Pat. No. 4,851,298 entitled "Multi-Layer Tube Of A Muffler For An Internal Combustion Engine" was issued Jul. 25, 1989. The Fukuda patent shows sheets 18 and 20 which are spot welded to themselves and are interconnected at a coupling portion 22. Fukuda U.S. Pat. No. 4,793,544 entitled "Method Of Producing A Multi-Layer Tube Of A Muffler" issued Dec. 27, 1988. The second mentioned Fukuda patent also discloses sheets 18 and 20 which are spot welded to themselves. Roberts U.S. Pat. No. 4,333,545 entitled "Back-Fire Resistant Lock Seam For Muffler Shells" issued Jun. 8, 1982. This disclosure teaches a muffler construction wherein a tongue 24 is spot welded to a portion of the wrap.
The typical and well-known construction of vehicular mufflers presents certain problems. In many instances, there is a considerable amount of shell noise between the two wraps of the shell. The noise is sometimes referred to oil canning. This is a phenomenon wherein the inner wrap or outer wrap vibrates due to pressure pulsations, temperature differences, thermal expansion and stress built up in the muffler body.